Just got in some Hitec servos. The stock JR's were mounted from factory using the grommets with metal inserts. If I try to mount the Hitec servos using the Hitec supplied grommets and metal inserts, the inserts are smaller inside diameter than the stock mounting screws are. I think the screws could be worked in, but those metal inserts would be deformed somewhat by the larger screw. If I try to use the JR grommets and metal inserts they don't fit the mounting holes of the Hitec servo, since the Hitec mounting holes are smaller than a JR.

I used the factory RTR brass inserts in the hitech ears. They fit the grommet is rubber and will expand just push it through, and mine where not bigger than the ears, so fit perfect once I pushed them through the grommet.

If you don't want to try this just use the grommet by itself but use a washer on the screw so that you cover more surface area of the grommet.